Duke Casimir I of Poland, also known as Casimir the Restorer, was a significant figure in Polish history during the 11th century. He was born around 1016 and became the Duke of Poland in 1039. His reign is noted for the restoration of the Polish state after a period of fragmentation and foreign domination. Casimir I worked to reunite the divided territories of Poland and strengthen its political structure. He is credited with promoting Christianity and supporting the Catholic Church, which helped to solidify the cultural and religious identity of the Polish people during his rule.